1. FIELD OF THE INVENTION
Various types of manufacturing processes are known in which the starting materials are introduced into the furnace while cold or at ambient temperature by the use of either continuously or discontinuously operating devices. Such devices are frequently protected by a hydraulic or other cooling apparatus which absorbs the heat from the furnace and additionally intensifies the cooling of the materials introduced into the furnace. In these methods, the starting materials are subjected to heating only after they have been introduced into the furnace where they receive, at high temperature, the quantities of heat necessary for melting them, for ensuring completion of the endothermic reactions, and for imparting thereto sufficient fluidity to ensure homogenization and refining of the resulting molten glass mass. It has been observed in glass making that the greater part of the heat delivered to the starting materials is directed to increasing the temperature of the starting materials rather than to producing the desired endothermic reactions. In most known methods, the starting materials are deposited on top of the molten bath and are subjected to radiation from the flames circulating with great turbulence above them. Since the newly-introduced materials are poor conductors of heat, the heat exchanger is poor, which slows the melting process, thus requiring greater quantities of heat.
The present invention especially relates to increasing the fuel efficiency and output of glass melting installations, and provides means whereby a glass melting furnace may be operated continuously and uniformly at full capacity or beyond, if desired. A method is provided for continuing the preheating of thoroughly-mixed, moisture-containing, glass-forming constituents upon interruption of gravity flow through a tubular heat exchanger before the constituents are supplied to the glass melting furnace. The method preferably utilizes the heat of the waste gases from the melting furnace in such preheating of the glass-forming constituents and effects continuous passage of the glass-forming batch mixture through the preheater by rapidly cooling the preheater tubes when flow is stopped or discontinued for any reason. The method is of special utility whether or not the batch mixture contains cullet.
The invention comprises an improved process to accomplish the aforesaid objects, and in the provision of an improved procedure for maintaining the continuous flow by gravity of the heated glass mixture in a tubular heat exchanger, as more fully set forth in the following specification, and as particularly pointed out in the appended claims.
The provision of the preheater for the glass mixture enables the utilization, for preheating the same, of the heat in the hot waste gases from the melting furnace which otherwise would go to waste up the stack. While the use of hot waste gases is preferred to operate the preheater, preheated air from the furnace heat-recovery "checkers" area which is usually used for combustion, or a supplemental heat source such as an oil or gas burner, alone or in combination, may be used. Also, the provision of the preheater, continuously delivering glass batch mixture at a proper predetermined elevated temperature, to a furnace, which is used with either a continuous or batch process, permits more uniform operation of the furnace with a significant increase in fuel efficiency during operation, and in the out-put of the furnace. The continued operation of a gravity-operated tubular heat exchanger having a plurality of spaced-apart, open-ended tubes, upon stoppage of flow for any reason, is often hampered by pluggage of the tubes. When the particulate material remains stationary in the tubes, a marked change in the coefficient of friction between the particulate material and the tubes occurs, and the material will no longer continue to freely slide by gravity. The present method obviates such difficulties.
2. DESCRIPTION OF PRIOR ART
There is a considerable number of earlier-issued U.S. patents which deal with initially preheating the glass batch mixture prior to its delivery into the glass furnace. U.S. Pat. No. 3,607,170 to Malesak discloses method and apparatus in which the glass batch mixture is preheated in a non-oxidizing atmosphere while being advanced in a given direction through a preheating zone of a tunnel kiln. A mixture of glass powder and foaming agent is delivered into a hopper having a series of tubes through which the mixture passes.
U.S. Pat. No. 3,172,648 to Brichard relates to preheating of pulverous materials in which the flow of the fumes in the preheating zone is in direct contact with the glass forming ingredients, such contact causing an entrainment of dust in the emitting fumes.
U.S. Pat. No. 4,045,197 to Tsai et al relates to apparatus and method for recovering the waste heat from the exhaust gases of a glass melting furnace and transferring the same by heat pipes to an enclosure in which incoming glass batch materials are preheated prior to being fed to a furnace for melting. The heat pipes contain metallic sodium as the working fluid.
U.S. Pat. No. 3,788,832 to Nesbitt et al, and U.S. Pat. No. 3,880,639 to Bodner et al, owned by the same common assignee as the present application, both relate to the preheating of agglomerated glass batch materials by direct contact with a gaseous effluent being exhausted from a glass melting furnace.
U.S. Pat. No. 3,185,554 to Sweo et al relates to a method of preheating glass batch materials by independent heating means other than exhausted effluent so that there is no unpredictable relationship between varying amounts of waste heat and the amount of heat provided for preheating unmelted batch materials.
A considerable number of other U.S. patents relate to the direct heat exchange between incoming batch materials and exhaust gases from a glass melting furnace. These U.S. Pat. Nos. are: 3,607,190--Penberthy, 4,026,691--Lovett, 3,526,492--Motsch, 3,350,312--Peyches, 1,543,770--Hilbert, 3,753,743--Kukuda, 1,610,377--Hitner, and 4,099,953--Rondeaux. Many techniques have been disclosed in the patent literature for direct and indirect heat exchange between hot exhaust gases from a glass melting furnace and incoming glass batch materials. However, none of the listed prior art references relate to a method for maintaining continuous flow of pulverous glass batch materials through a tubular heat exchanger wherein they are preheated during gravity flow through such heat exchanger having open-ended tubes.